1 module 8 unit iii " copyright 2002, information spectrum, inc. all rights reserved." how...

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Module 8Module 8

UNIT IIIUNIT III

"Copyright 2002, Information Spectrum, Inc. All Rights Reserved."

HOW TO PERFORM RCMHOW TO PERFORM RCMHOW TO PERFORM RCMHOW TO PERFORM RCM

ANALYTICAL METHODSANALYTICAL METHODSANALYTICAL METHODSANALYTICAL METHODS

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Module Preview:Module Preview:Module Preview:Module Preview:

• IntroductionIntroduction• IntroductionIntroduction

• Interval CalculationsInterval Calculations• Interval CalculationsInterval Calculations

IntroductionIntroductionIntroductionIntroduction

• Cautions and WarningsCautions and Warnings• Cautions and WarningsCautions and Warnings

• Review and SummaryReview and Summary• Review and SummaryReview and Summary

• Cost CalculationsCost Calculations• Cost CalculationsCost Calculations

• Spreadsheet ExerciseSpreadsheet Exercise• Spreadsheet ExerciseSpreadsheet Exercise


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Module Module Objective:Objective:Module Module

Objective:Objective:

This module will provide information on This module will provide information on different analytical methods that may be different analytical methods that may be used in RCM analysis: used in RCM analysis:

1.1. Introduce some methods of determining Introduce some methods of determining task intervalstask intervals

2.2. Demonstrate the cost equations used by Demonstrate the cost equations used by the IRCMS softwarethe IRCMS software

3.3. Discuss limitations and cautions Discuss limitations and cautions associated with these methodsassociated with these methods

IntroductionIntroductionIntroductionIntroduction


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Interval CalculationsInterval CalculationsInterval CalculationsInterval Calculations

• Inspection Interval (I) (Ref: NAVAIR 00-25-Inspection Interval (I) (Ref: NAVAIR 00-25-403):403):

I = PF/nI = PF/nWhere: Where:

PF PF = interval from potential failure to functional = interval from potential failure to functional failurefailuren n = number of inspections during PF interval= number of inspections during PF interval

Where:Where:• Using Pacc (safety or non-safety)Using Pacc (safety or non-safety)

n = ln (Pacc) / ln (1-theta)n = ln (Pacc) / ln (1-theta)

• Using Cost optimization (non-safety)Using Cost optimization (non-safety)n = n = ln [ (-MTBF*Ci/PF)/((Cnpm-Cpf)*ln(1-theta)) ]ln [ (-MTBF*Ci/PF)/((Cnpm-Cpf)*ln(1-theta)) ]nn

ln(1-theta)ln(1-theta)

On-condition On-condition Task:Task:



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Derivation:Derivation: n = ln (Pacc) / ln (1-theta)n = ln (Pacc) / ln (1-theta)

Theta Theta = probability of detecting a Potential = probability of detecting a Potential Failure in Failure in one inspection assuming it existsone inspection assuming it exists

(1-theta) (1-theta) = probability of not detecting a Potential = probability of not detecting a Potential Failure in one inspection assuming it Failure in one inspection assuming it

existsexists(1-theta)(1-theta)nn = probability of not detecting a Potential = probability of not detecting a Potential

Failure Failure in “n” inspections assuming it existsin “n” inspections assuming it exists

• Goal of inspection is Goal of inspection is (1-theta)(1-theta)nn < Pacc < Pacc• Longest inspection meeting this criteria Longest inspection meeting this criteria

would occur at would occur at (1-theta)(1-theta)nn = Pacc = Pacc• Solving for n: Solving for n:

n = ln (Pacc) / ln (1-theta)n = ln (Pacc) / ln (1-theta)




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• If an inspection may require deferral of If an inspection may require deferral of the corrective action when found the the corrective action when found the inspection interval should allow for the inspection interval should allow for the deferral time (Tc)deferral time (Tc)

• Applicable in continuously operating Applicable in continuously operating equipment or processes or where equipment or processes or where repair deferred and use continuesrepair deferred and use continues

• Mathematically:Mathematically:

I = (PF/n)-TcI = (PF/n)-Tc

where: where: Tc = Time needed to perform corrective Tc = Time needed to perform corrective

actionaction




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LIMITATIONSLIMITATIONS

• Method is conservative Method is conservative

• Based on assumption that potential failure Based on assumption that potential failure always existsalways exists

• If more precise interval is desired, actual If more precise interval is desired, actual

failure rate and distribution needs to be failure rate and distribution needs to be considered in more detail considered in more detail

• As more precision is pursued, loss of As more precision is pursued, loss of

conservatism must be weighed against conservatism must be weighed against confidence in the data sources to ensure confidence in the data sources to ensure adequate levels of protectionadequate levels of protection





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n = n = ln [ (-MTBF*Ci/PF)/((Cnpm-Cpf)*ln(1-theta)) ]ln [ (-MTBF*Ci/PF)/((Cnpm-Cpf)*ln(1-theta)) ]nn

ln(1-theta)ln(1-theta)

Where:Where:Ci Ci = Cost of one inspection= Cost of one inspectionCnpm Cnpm = Cost of No PM = Cost of No PM

= Cost of Corrective Maint + Cost Lost Op = Cost of Corrective Maint + Cost Lost Op timetimeCpf Cpf = Cost of repairing a PF= Cost of repairing a PF

See NAVAIR 00-25-403See NAVAIR 00-25-403




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• Statistical (Weibull) or empirical (Test or Statistical (Weibull) or empirical (Test or sampling) methodssampling) methods

• Beyond the scope of this courseBeyond the scope of this course

Hard-Time Task:Hard-Time Task:Hard-Time Task:Hard-Time Task:


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Interval CalculationsInterval CalculationsInterval CalculationsInterval CalculationsFailure Finding TaskFailure Finding Task:Failure Finding TaskFailure Finding Task:

• Inspection Interval (I) (Ref: NAVAIR 00-25-Inspection Interval (I) (Ref: NAVAIR 00-25-403):403):

Determine by setting PDetermine by setting Pmfmf = P= Paccacc

Where:Where:

PPmfmf = P = Phiddenhidden x P x Padditionaladditional

PPmfmf = Probability of multiple failure = Probability of multiple failure

occurringoccurring

PPhiddenhidden = Probability of the hidden failure = Probability of the hidden failure

occurringoccurring

PPadditionaladditional = Probability of an additional failure = Probability of an additional failure

occurringoccurring


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Interval CalculationsInterval CalculationsInterval CalculationsInterval CalculationsFailure Finding Task:Failure Finding Task:Failure Finding Task:Failure Finding Task:

Assuming a constant failure rate for each term:Assuming a constant failure rate for each term:

P P = 1 - e = 1 - e-t / MTBF-t / MTBF

(1) (1) PPmfmf = P= Phiddenhidden x P x Padditionaladditional

= (1 = (1 - e- e-t / MTBF-t / MTBFhiddenhidden) x (1 ) x (1 - e- e-t / MTBF-t / MTBFadditional additional ))

(2) (2) PPmf mf = = PPaccacc(t) = (1 (t) = (1 - e- e-t / MTBF-t / MTBFacceptableacceptable) )


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Combining equations (1) and (2)Combining equations (1) and (2)

(3) (3) (1 (1 - e- e-t / MTBF-t / MTBFacceptableacceptable) = (1 ) = (1 - e- e-t / MTBF-t / MTBFhiddenhidden) x (1 ) x (1 - e- e-t / MTBF-t / MTBFadditionaladditional ))

Two unknowns: MTBFTwo unknowns: MTBFacceptable acceptable and t and t

To determine MTBFTo determine MTBFacceptableacceptable solve solve (1 (1 - e- e-t / MTBF-t / MTBFacceptableacceptable ) for a ) for a

known Pacc and tknown Pacc and tFor example using a program established Pacc(at t=1) For example using a program established Pacc(at t=1)

= .000001= .000001

Finally Equation (3) can be solved for t which is used for IFinally Equation (3) can be solved for t which is used for INote: equation (3) can only be solved iteratively (use the Note: equation (3) can only be solved iteratively (use the

spreadsheet)spreadsheet)

For economic/operational consequences, must beFor economic/operational consequences, must becost-effective cost-effective


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LIMITATIONSLIMITATIONS

• Method assumes hidden and additional Method assumes hidden and additional

failures are random and failures are random and independentindependent

• Assumption of randomness is usually Assumption of randomness is usually

conservativeconservative

• If failures are dependent method may NOT If failures are dependent method may NOT

be conservative!be conservative!

• If hidden failure is not random to a high If hidden failure is not random to a high

degree another task option such as Hard time degree another task option such as Hard time

may be more appropriatemay be more appropriate


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Overview:Overview:Overview:Overview: Cost CalculationsCost CalculationsCost CalculationsCost Calculations

• IRCMS Cost Analysis provides a means to IRCMS Cost Analysis provides a means to compare compare relativerelative cost of each task and cost of each task and other failure management optionsother failure management options

• Normalized to one unit of operating timeNormalized to one unit of operating time

• Typical Cost per Unit Op time Typical Cost per Unit Op time = Cost of one task / task interval= Cost of one task / task interval+ Cost of repairs associated with task/period + Cost of repairs associated with task/period

between repairsbetween repairs


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Service/Lube:Service/Lube:Service/Lube:Service/Lube: Cost CalculationsCost CalculationsCost CalculationsCost Calculations

• Service/Lube TaskService/Lube Task

SLSLOPOP = Service/lubrication task cost per operating = Service/lubrication task cost per operating

timetime

SLSLOPOP = C= CSLSL / I / ISLSL

Where:Where:

CCSLSL = = Cost Of One SL TaskCost Of One SL Task= = ((MHsMHs to perform task) x (cost per MH) + to perform task) x (cost per MH) +

material cost material cost

IISLSL = = Task IntervalTask Interval


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On-Condition:On-Condition:On-Condition:On-Condition: Cost CalculationsCost CalculationsCost CalculationsCost Calculations• On-condition TaskOn-condition Task

OCOCOP OP = On-condition task cost per operating time = On-condition task cost per operating time

OCOCOPOP = ((C= ((C

OCOC / I / IOCOC) *(L - (I) *(L - (I

II-I-IOCOC)) / L) + C)) / L) + C

R R / MTBF/ MTBF

Where:Where:

CCOC OC = Cost of one OC Task (Not including repair costs)= Cost of one OC Task (Not including repair costs)

(MHs to perform task) * (cost per MH) + cost of materials (MHs to perform task) * (cost per MH) + cost of materials L L = = Item Design LifeItem Design Life

IIII = = Initial Inspection IntervalInitial Inspection Interval (Inspection Threshold) (Inspection Threshold)

IIOCOC = = Task IntervalTask Interval

MTBF MTBF = = Mean time between failures (both potential and functional with Mean time between failures (both potential and functional with task in place)task in place)

CCRR = = Average Repair CostAverage Repair Cost. .

Include all failures (potential and functional failures) Include all failures (potential and functional failures) Include secondary damage Include secondary damage Include the cost of multiple failures in the functional failure portion of the Include the cost of multiple failures in the functional failure portion of the

costcost Include operational impact if it has been converted to a "cost"Include operational impact if it has been converted to a "cost"


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Hard-Time:Hard-Time:Hard-Time:Hard-Time: Cost CalculationsCost CalculationsCost CalculationsCost Calculations

• Hard-Time TaskHard-Time TaskHTHTOP OP = Hard time task cost per operating time= Hard time task cost per operating time

HTHTOPOP = [C= [CHTHT (S) + C (S) + CRR (1-S)] / [(S) I (1-S)] / [(S) IHT HT + (1-S) K I+ (1-S) K IHTHT]]

Where:Where:

CCHTHT = = Cost Of One HTCost Of One HT

= (= (MHsMHs to perform task) x (cost per MH) + cost of to perform task) x (cost per MH) + cost of materialsmaterialsS S = Percentage of items that survive to the hard time limit= Percentage of items that survive to the hard time limit

IIHTHT = = Task IntervalTask Interval

K K = = Premature Failure FactorPremature Failure Factor = Average age of premature failures as a percentage of I= Average age of premature failures as a percentage of I

HT.HT.

((NoteNote: K I: K IHT HT is used to estimate MTTF of premature failures.)is used to estimate MTTF of premature failures.)

CCRR = Average Repair Cost if HT not accomplished. = Average Repair Cost if HT not accomplished.

Ensure secondary damage is includedEnsure secondary damage is includedFor hidden functions include the cost of multiple failures. For hidden functions include the cost of multiple failures. Include operational impact if converted to a "cost"Include operational impact if converted to a "cost"


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Failure Finding:Failure Finding:Failure Finding:Failure Finding: Cost CalculationsCost CalculationsCost CalculationsCost Calculations• Failure FindingFailure Finding

FFFFOPOP = Failure Finding task cost per operating time= Failure Finding task cost per operating time

FFFFOPOP = C= CFFFF / I / IFFFF + C + CRR / MTBF / MTBF

Where:Where:

CCFFFF = = Cost Of One Inspection Cost Of One Inspection

= (= (MHsMHs to perform task) x (cost per MH) + cost of to perform task) x (cost per MH) + cost of

materialsmaterials

IIFFFF = = Task IntervalTask Interval

MTBF = MTBF = Mean time between failures (with task in place) Mean time between failures (with task in place)

CCRR = = Average Repair Cost.Average Repair Cost. • Average cost of repairing the functional failures found by the Average cost of repairing the functional failures found by the

inspection and those that become evident by multiple failures not inspection and those that become evident by multiple failures not

prevented. prevented. • Include operational impact if it has been converted to "cost".Include operational impact if it has been converted to "cost".


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• No PM (Run to Failure)No PM (Run to Failure)

NONOOPOP = “No PM” cost per operating time = “No PM” cost per operating time

NONOOPOP = C = CRR / MTBF / MTBF

Where:Where:CCRR = = Average RepaiAverage Repair r CostCost

• Average cost to repair the functional failure Average cost to repair the functional failure and secondary damage. and secondary damage.

• For hidden functions, include the cost of For hidden functions, include the cost of multiple failures. multiple failures.

• Include operational impact if it has been Include operational impact if it has been converted to "cost".converted to "cost".

MTBF = MTBF = Mean time between failures (with no task Mean time between failures (with no task in in place) place)


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• Other Action Other Action

OAOAOPOP = “Other action” cost per operating time = “Other action” cost per operating time

OAOAOPOP = C = COAOA / L / LRR

Where:Where:

CCOA OA = Total cost to develop and = Total cost to develop and

implement “Other Action”implement “Other Action”

LLRR = = Total Total remaining life of remaining life of

system/fleetsystem/fleet


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Overview:Overview:Overview:Overview: Cautions and Cautions and WarningsWarnings

Cautions and Cautions and WarningsWarnings

• All methods are approximationsAll methods are approximations• Subject to changes in dataSubject to changes in data

• Consider sensitivityConsider sensitivity• Schedule follow-up validation of assumptions (Age Schedule follow-up validation of assumptions (Age

Exploration)Exploration)

• User is responsible for understanding the limits and User is responsible for understanding the limits and

applicability of each method applicability of each method

• Not every failure mode requires in depth analytical Not every failure mode requires in depth analytical

analysis (pick your battles)analysis (pick your battles)• Estimates can be used in many casesEstimates can be used in many cases

Note:Note: Equations discussed on the following slides describe Equations discussed on the following slides describe the current methods provided in NA-00-25-403. Users the current methods provided in NA-00-25-403. Users should stay abreast of differences between latest NA-00-should stay abreast of differences between latest NA-00-25-40325-403 methods and those used in IRCMSmethods and those used in IRCMS


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Overview:Overview: Spreadsheet Spreadsheet ExerciseExercise

Spreadsheet Spreadsheet ExerciseExercise

• ExerciseExercise


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Overview:Overview:

Analytical MethodsAnalytical MethodsAnalytical MethodsAnalytical Methods



• ExerciseExercise

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Review and SummaryReview and SummaryReview and SummaryReview and Summary

• Module ObjectiveModule Objective• Module ObjectiveModule Objective

• Review and SummaryReview and Summary• Review and SummaryReview and Summary

• IntroductionIntroduction• IntroductionIntroduction

• Interval CalculationsInterval Calculations• Interval CalculationsInterval Calculations

• Cautions and WarningsCautions and Warnings• Cautions and WarningsCautions and Warnings

• Cost CalculationsCost Calculations• Cost CalculationsCost Calculations

• Spreadsheet ExerciseSpreadsheet Exercise• Spreadsheet ExerciseSpreadsheet Exercise


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End of Module up next……..

Unit IV Module 1Packaging

End of Module up next……..

Unit IV Module 1Packaging

1 module 8 unit iii " copyright 2002, information spectrum, inc. all rights reserved." how...

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